The determination of the acoustic properties of fluids in containers or flowing through conduits and pipes is important In many industries, in particular in oil production, as these properties may be used to determine fluid composition. Typically, acoustic measurements (for example, sound speed and sound absorption in liquids) are made with sensors attached to the pipe through special windows machined into the pipe wall where the sensor elements make physical contact with the fluid or are mounted directly in the fluid. In such situations, the sensors or the windows are subject to fouling by the fluid, making long-term operation and maintenance difficult. Moreover, if a sensor is placed inside the fluid or intrudes into the liquid through the wall, it can affect the flow pattern and contaminate the measurements that are sensitive to a disruption of the flow pattern.
High voltage pulsed signals having 10 μm is duration have been used to excite sound waves in an ultrasonic transducer attached to a curved delay line that conforms to the exterior curvature of a pipe, the sound waves being detected by a second transducer after traversing through the fluid in the pipe. The transit time of the pulses is measured by threshold detection of the received signal, which is difficult due to multiple reflections in the container wall and also due to propagation of sound through the wall itself. The average of 100 signals is required for proper threshold detection for a transit time measurement from which fluid sound speed and subsequently fluid composition are determined.